Precautions For Dmac; Write To Dmae Bit In Dmicon Register (I = 0, 1) - Renesas M16C/60 Series Hardware Manual

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M16C/6N5 Group

1.6 Precautions for DMAC

1.6.1 Write to DMAE Bit in DMiCON Register (i = 0, 1)

When both of the conditions below are met, follow the steps below.
Conditions
• The DMAE bit is set to "1" again while it remains set (DMAi is in an active state).
• A DMA request may occur simultaneously when the DMAE bit is being written.
Step 1: Write "1" to the DMAE bit and DMAS bit in DMiCON register simultaneously (Note 1) .
Step 2: Make sure that the DMAi is in an initial state (Note 2) in a program.
If the DMAi is not in an initial state, the above steps should be repeated.
Note 1: The DMAS bit remains unchanged even if "1" is written. However, if "0" is written to this bit, it
is set to "0" (DMA not requested). In order to prevent the DMAS bit from being modified to "0,
"1" should be written to the DMAS bit when "1" is written to the DMAE bit. In this way the state
of the DMAS bit immediately before being written can be maintained.
Similarly, when writing to the DMAE bit with a read-modify-write instruction, "1" should be
written to the DMAS bit in order to maintain a DMA request which is generated during execution.
Note 2: Read the TCRi register to verify whether the DMAi is in an initial state. If the read value is
equal to a value which was written to the TCRi register before DMA transfer start, the DMAi is in an
initial state. (If a DMA request occurs after writing to the DMAE bit, the value written to the
TCRi register is "1".) If the read value is a value in the middle of transfer, the DMAi is not in an
initial state.
Rev.1.00 2003.05.30 page 8
1.6 Precautions for DMAC